2 teeth on the rear

[solman]

I finally got my new 112 link chain and 47 tooth sprocket installed.  What a difference!  The acceleration is great and it got rid of the occasional low rpm stumble off the line.  My biggest problem now is to force myself to let off the throttle now.  I want to play too much now. BTW, I notice very little difference in cruising rpm as well.

[bikeb4cage]

Hey Solman - you recommend the 47T?  I have stock gearing on the B12, and truth be told, I miss reving the motor like on my B6 - by the time your get deep into the revs in second gear (on the B12) the speed has already crept up a bit - seems like a lower overall gearing setup would be fun - any downside?  other than a little MPG and speedo/odo error...

thanks
Jay

[solman]

No downsides at all.  Gas is the same, torque application is better, only raises the rpm's about 200 while cruising.  Probably helped the speedo error since it is a bit optimistic.  Only thing different is that if you have a newer chain, you may have to get a new chain and add two links for it  to fit.  If you use the stock 110 link with two added teeth, it won't fit. So use 112 links for a new chain.  My Friend who also has a B12 refuses to got back to stock rear sprocket.

[billincentraljersey]

Probably helped the speedo error since it is a bit optimistic.

Solman,

Maybe you should revisit that.  I think the optimistic speedo get worst with lower gearing.  your odo will also speed up as well.  I read that stock odo usually are fairly accurate.  I was thinking of increasing my gear ratio, +3 teeth at the rear, to LOWER the RPM while crusing long distance.  The side benefit is that it corrects the speedo back to what it should be, 5mph less at around 70mph.  The bad side is that the odo will then be slower.  Unfortunately, there is no easy way to separate the link between the odo and the speedo, yet.

[solman]

I was thinking of increasing my gear ratio, +3 teeth at the rear, to LOWER the RPM while crusing long distance.

Maybe you should rethink that!  Adding 3 teeth to the rear will increase your rpm's at cruising speed.  On the other thing about speedo's being accurate, I don't think so.  They tend to be optimistic around 5 mph at cruising speed.  I have read that they do this on purpose.  Don't know about if it is true or not.  If you want a true speed, get a gps.

[Bob Holland]

According to the gearing caculator
15/45 60.4 mph = 3500 rpm
15/47 60.3 mph = 3650 rpm
15/48 60.6 mph = 3750 rpm
That is using 24.85 inches for rear tire diameter, which is the only varient.
For 2 gen and newer
If the speedo is already off to the high side, then it will be off a little more with 15/47

ratio---------True MPH----------Speedo
15/45----------60.4---------------65
15/47----------60.3---------------68
16/48----------60.6---------------70
This does not apply if the speedo runs off the front wheel.  

[billincentraljersey]

I was thinking of increasing my gear ratio, +3 teeth at the rear, to LOWER the RPM while crusing long distance.

Maybe you should rethink that!  

Solman,

You are absolutely correct.  I meant to type -3 teeth at the rear.  That will decrease the RPM for the same speed.

I agree with the speculation that the factory make the speedo optimistic.  Too bad the odo is accurate and link to the speedo.  Correcting the speedo will screw up the odo.  Someone here (or ws it at the MS forum?) checked with  a GPS and said it was about 5mph optimistic at crusing speed.

[billincentraljersey]

BHolland, Solman,

Seems like you guys have been thinking about this a lot longer than I have.  If I go forward with my -3T at the rear for the B1250, I figured it would bring my speedo close to it's actual speed.  If indicated speed of 75 is actually 70mph.  

Did I get this right?  

75mph indicated * 45T new / 48T old = 70.3mph actual

[solman]

BHolland, Solman,

Seems like you guys have been thinking about this a lot longer than I have.  If I go forward with my -3T at the rear for the B1250, I figured it would bring my speedo close to it's actual speed.  If indicated speed of 75 is actually 70mph.  

Did I get this right?  

75mph indicated * 45T new / 48T old = 70.3mph actual

Gearing charts may say one thing, but GPS don't lie.  I don't recall ever seeing any bike that didn't have an optimistic speedo.  I remember seeing an article once on the Haybusa where the indicated was something like 201 mph and his actual speed was 193 mph on radar.

[Bob Holland]

I read that the factories set the tachs high so that when you hit redline by the tach, you are actually a few hundred rpms below. They set the speedo to be perty close to the tach. And every one I have ever checked was off to the high side. I have a GPS and the dyna shift light and my 98 bandit tach and speedo are off about 10%
I believe that the stock gearing on the B1250 is 18/45

------1st---2nd---3rd--4th--5th--6th
 RPM   MPH   MPH   MPH   MPH   MPH   MPH
 1,500  _9.4  14.0  18.6  22.1  24.9  26.9
 2,000    12.5  18.7  24.8  29.5  33.2  35.9
 2,500    15.6  23.4  31.0  36.9  41.5  44.9
 3,000    18.8  28.0  37.2  44.3  49.8  53.9
 3,500    21.9  32.7  43.4  51.6  58.1  62.9
 3,750    23.4  35.0  46.5  55.3  62.2  67.4
 4,000    25.0  37.4  49.7  59.0  66.3  71.9

B1250 with 18/42

 1,500   10.0  15.0  19.9  23.7  26.7  28.9
 2,000    13.4  20.0  26.6  31.6  35.5  38.5
 2,500    16.7  25.0  33.2  39.5  44.4  48.1
 3,000    20.1  30.0  39.9  47.4  53.3  57.7
 3,500    23.4  35.0  46.5  55.3  62.2  67.4
 3,750    25.1  37.5  49.9  59.3  66.6  72.2
 4,000    26.8  40.0  53.2  63.2  71.1  77.0

Dunlop 207-180/55ZR17 Rear
Tire Diameter (inches) 24.85
Tire Circumference (Inches)   78.07

[bikeb4cage]

put a 14T (45 T rear) on my bike, to check out the feel - what a difference - feels like a new bike, love the higher revs -eventually will replace the chain with a 112 link and a 15T/47T.  It rips pretty good through the gears now with the 14T, I am sure the top end is hurt a bit, but not too concerned about that.

Jay

[Bob Holland]

I ran 13/52 on my GSXR 1216 dragbike, It would top out in 5th gear, 10,500 rpms, just as I crossed the 1/4 mile line, at 135 mph. It was like being shot out of a cannon when you left the starting line.